Two experiments evaluated the effects of preemergence herbicides on pampas grass [Cortaderia selloana (Schult. and Schult. f.) Asch. and Graebn.] growth. Herbicides were applied 1, 15, or 30 days after potting (DAP) from 36-cell packs into 3.8 liter (#1) containers. Ronstar (oxadiazon) applied at the manufacturer's recommended rate caused little or no injury when applied 1 or 15 DAP. Factor 65 WG (prodiamine) applied 1 DAP suppressed root growth compared to control plants; however, when applied 15 or 30 DAP root ratings of Factor treated plants were similar to control plants 60 and 75 DAP. Plant height at 90 DAP was about 10% greater when the herbicide application was delayed 30 DAP, compared to plants treated 1 DAP. In experiment 2, plant height and root ratings were greater when herbicides were applied 30 DAP than when applied 1 DAP. Pendulum 2G (pendimethalin), Pendulum 60 WDG (pendimethalin), and Factor 65 WG (prodiamine) suppressed root growth in the upper 5.1 cm (2 in) and lower 10.2 (4 in) of container medium. Plants treated with Factor 65 WG or Pendulum 60 WDG generally had the highest percent lodging and the most club roots in both experiments; Ronstar was the only herbicide that did not cause lodging or club root formation.

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Author notes

2Graduate Assistant.

3Professor.

4Associate Professor.